A Wind turbine generator (WTG) is used to gather wind energy and to transform the energy into another form of energy. For this purpose most wind turbine generators include a shaft which in one end is coupled to a rotor comprising a number of wind turbine blades. In the opposite end, the shaft is normally connected to a driven wind turbine part. This driven wind turbine part may be an entrance member of a gearbox or an entrance member or torque transferring member of an electric energy generator. Upon rotation of the shaft, in response to wind acting on the blades, energy can be transformed.
In order to control precisely the rotation of the shaft while also supporting the shaft, the shaft is supported by a number of bearings positioned along the shaft. These bearings are provided in order to transfer loads from the shaft and into a supporting structure of the bearings and the bearings are provided for enabling rotation torque of the shaft to be transferred into the gearbox and/or the generator.
The main loads are typically in an axial direction of the shaft as well as, and e.g. due to a weight of the rotor, in direction of gravity or substantially in the direction of gravity. In a so-called horizontal axis wind turbine, as embodied herein, such loads are typically transferred further on into a frame like structure in a nacelle of the wind turbine and from there on via a yawing system into a tower of the wind turbine and into a foundation in the ground.
As the size of wind turbines tend to increase, the loads acting on one or more of the bearings and their respective support structure also tend to increase.
The forces acting on the shaft are, in addition to the main load directions mentioned, also present in directions which are radial to the shaft but not substantially in the direction of gravity. Such forces are among others due to the dynamical variation of the wind, both in direction and amplitude, and due to a yawing movement of the nacelle.
Various bearing solutions and systems have been seen in order to control precisely the rotation of the shaft while providing a steady and precise support of the shaft of the wind turbine. In view of the present inventor and applicant these solutions may be seen to have one or more of the following examples of disadvantages.
Some solutions tend to provide a bearing system of one or more bearings and their supports which have proven to be so heavy and/or to be provided with relatively large dimensions that installation or servicing of these bearing systems have proven to be difficult and/or quite time consuming. Still further such solutions, where a single bearing with supporting structure may weigh around 600-1200 kilos, have proven quite costly to produce.
Some solutions tend to necessitate a very precise positioning of bearing parts relative to the supporting structure and/or tend to require costly and/or very precise manufacturing tolerances for both the bearing and the support, in order to precisely control and support the shaft and the loads acting on the shaft.
Still further and in some solutions, upon servicing a bearing, it has proven difficult and/or time consuming to exchange the bearing, i.e. to detach the bearing from its supporting structure. In some cases this is at least partly due to corrosion.
Some solutions have proven that they were not able to withstand the loads acting on the shaft, or have at least proven that these solutions were not able to withstand the loads in a precisely controlled manner in an amount of years as initially assessed and yet some solutions have additionally or alternatively proven to be too expensive when considering their overall effectiveness.